We have previously reported that a population of afferent nerves from the arterial baroreceptors contain the neuropeptide substance P (SP). These nerves were traced to the nucleus of the tractus diagonalis (NTS) of the medulla oblongata of the hindbrain. Several studies have focused attention on the possible pathogenesis of hypertension by central catecholamine alterations in spontaneously hypertensive (SHR) rats. The present experiment deals with two substrains of the Sabra rat, one of which is genetically predisposed to develop hypertension when fed on a DOCA salt diet (SBH), while the other is hypertension resistant (SBN). In the present experiment SP, catecholamine and vasopressin were studied in the NTS of these rats. Higher concentrations of NE, Epi were observed in the NTS of the SBH strain as compared to the control (SB) or hypertension resistant strain (SBN). The SB was significantly greater than the SBN. SP levels were higher in the SBH and SBN as compared with the SB strain. Vasopressin was higher in SBH and lower in SBN than SB. The significance of a similar directional change for SP in the SBH and SBN strain is unknown. The changes in catecholamines and vasopressin do, however, carrelate with the predisposition for hypertension. Whether the changes observed in the catecholamine and peptide systems are causitive or adaptive phenomena in the pathogenesis of hypertension susceptibility or resistance awaits further investigation.